U.S. Route 231 is a parallel route of U.S. Route 31. It currently runs for 912 miles (1,467 km) from St. John, Indiana, at U.S. Route 41 to south of U.S. Route 98 in Downtown Panama City, Florida.

One of its most notable landmarks is the William H. Natcher Bridge, a nearly mile-long cable-stayed bridge that connects Rockport, Indiana, to Owensboro, Kentucky, spanning the Ohio River.

In Florida, US 231 is paired with unsigned State Road 75. The southern terminus is at Business US 98 (unsigned State Road 30) in downtown Panama City. The highway is carried by Harrison Avenue until its intersection with US 98. Continuing north, US 231 passes through Youngstown, Fountain, Alford, Cottondale, and Campbellton before entering Alabama. Major intersections include Business US 98, US 98, SR 77, SR 20, Interstate 10, US 90, SR 73, SR 273, and SR 2.

In Alabama, US 231 is paired with unsigned State Route 53 from Huntsville to Dothan. From the Tennessee state line to Huntsville, and from Dothan to the Florida state line, this route is paired with unsigned State Route 1. From the Tennessee line to Huntsville, US 231 pairs with US 431. In Harpersville US 231 follows US 280 east. Just south of Sylacauga US 231 branches off southward again as its own route to Montgomery. US 231 is referred to as Memorial Parkway throughout Huntsville and Madison County.

In Dothan, there is a spur of US 231, Business US 231, which runs north–south directly through downtown Dothan from US 231 at the Ross Clark Circle. Until the 1980s, there were several other Business US 231 designations near and through the towns of Brundidge, Troy, and Montgomery.

Also, until the 1980s, there was an Alternate US-231 which ran north from the intersection/interchange with US-280 just south of Sylacauga, Alabama, northeastward through Sylacauga, Winterboro, and onto Talladega, Alabama. This routing was co-signed with Alabama State Route 21. From Talladega, Alternate US-231 ran northward co-signed with Alabama State Route 77 to just south of Lincoln, Alabama. There for a one-mile segment, Alternate US 231 ran along its own route just west of and parallel to Alabama State Route 77 until it reached an intersection with US-78 in the center of the small town of Lincoln, Alabama. There Alternate US-231 turned westward for nine miles co-signed with US-78 into Pell City, Alabama. There Alternate US-231 rejoined US-231. Alternate US-231 was decommissioned in the early 1980s.

Much of US 231 throughout north and central Alabama is a two-lane route. However, from just north of Wetumpka, Alabama, southward to the Florida state line the route is four lanes. Also, the section from the Tennessee-Alabama state line southward to Arab, AL, is also four lanes. In north and central Alabama, US 231 traverses the SW to NE ridgelines of the Appalachian Mountains as well as crossing several river valleys which provide some excellent natural scenery. Most of the four-lane segment south of Wetumpka, Alabama, to the Florida state line is along gently rolling countryside from several river and stream valleys onto the Gulf Coastal Plain.

US 231 pairs with 31E and continues to run south through the eastern Nashville metro area through the cities of Lebanon and Murfreesboro, and finally reaching Fayetteville until it crosses the Alabama state line. From Fayetteville to the Alabama line, US 231 pairs with US 431. The route is approximately 121 miles (195 km) from Tennessee's northern border to its southern border.

US 231 parallels Interstate 65 before reaching Bowling Green. From Bowling Green, US 231 closely parallels the William H. Natcher Parkway until it reaches Owensboro. At Owensboro, US 231 joins US 60 (also known as the Wendell H. Ford Expressway) around the city's east side, which it then follows to just north of Maceo. US 60 then leaves toward the east while US 231 turns to the north, leaving the state via the William H. Natcher Bridge across the Ohio River.

As of 2008, the Wendell H. Ford Expressway ends at a signalized intersection with US 60 that often experiences traffic backups during the morning and evening rush hours. The Kentucky Transportation Cabinet has plans to extend the expressway from the Kentucky 54 interchange northeastward to the present at-grade intersection of US 60/US 231 and Kentucky 2830. This project was originally to have been completed in 2010, although it was delayed due to budget concerns at the state level.

In October 2010, construction is underway between the western terminus of Kentucky State Route 2830 (the former route of U.S. 60) and Kentucky State Route 144 northeast of Owensboro. More construction is underway to connect the new hospital campus of the Owensboro Medical Health System (which is scheduled for completion in 2013) to the new highway. This work is being done close to the southeastern end of the proposed expressway extension, near Kentucky State Route 54.

In Indiana, US 231 has the distinction of being the state's longest continuous highway. It covers approximately 297 miles (478 km) in the Hoosier State. US 231 passes through the towns of Dale, Huntingburg, Jasper, and Loogootee before reaching Bloomfield. In Bloomfield, US 231 passes Shawnee Field, a local airport. US 231 slices through central Indiana before reaching Lafayette, where it runs just south of Purdue University. Next it winds northwest along Interstate 65 and then it splits off and terminates at US 41.

Indiana's Major Moves program, which derives its funding from the lease of the Indiana Toll Road to private interests, has made it possible for the state to build many new miles of roadway throughout the state. As part of this program, US 231 is currently being updated to a new-terrain four-lane highway from the Indiana-Kentucky border through Spencer County to Interstate 64. This segment of US 231 has been named the Abraham Lincoln Memorial Parkway.

As of April 2011, the Lincoln Parkway is complete from the Kentucky line to the interchange at I-64 and the bypass of Dale at the northernmost end of the project. It is a fully operational partial cloverleaf and the previous two-lane 231 overpass has been demolished. It has been replaced by a new four-lane overpass.

The section from SR 162 to Indiana State Highway 70 near Chrisney was the last to be opened, after a ribbon-cutting ceremony on March 15, 2011, much sooner than the original July 2011 projected date.

In addition to the Spencer County project, a four-lane bypass of the Dubois County cities of Huntingburg and Jasper is also in the planning stages, with completion tentatively scheduled for 2015.

U.S. Route 152 was commissioned in 1934, connecting Indianapolis with Hammond. It followed US 52 from Indianapolis to northwest of Lafayette, where it turned north to end at US 20 in Hammond. In 1938, the route was decommissioned, and became a southern extension of State Road 53 from northwest of Lafayette to Crown Point, a new State Road 152 from Highland to Hammond, and was simply dropped in favor of the overlapping US 52, State Road 8, and US 41 elsewhere. These parts of SR 53 and SR 8 became US 231 in 1952, when US 231 was extended north from Montgomery to US 41 south of St. John.